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Classroom activity Grade 7 Science

The Corvin Lake Nutrient Path: A Grade 7 Eutrophication Game

A grade 7 role-play where students move nutrient and oxygen tokens along a lake pathway to model fertilizer runoff, an algae bloom, and an oxygen crash.

Objectives

  1. Students will model how excess nutrients move from land into a lake.
  2. Students will explain how a nutrient overload lowers dissolved oxygen and affects fish.
  3. Students will describe how nutrients can be both a resource and a pollutant.

Vocabulary

Dissolved oxygen
Dissolved oxygen is the oxygen gas mixed into water that fish and other underwater animals breathe. Cold, moving water holds more oxygen than warm, still water.
Eutrophication
Eutrophication is what happens when a lake or bay gets overfed with nutrients: algae grows out of control, and when it dies and rots, the water loses the oxygen that fish need.

Also: nutrient, nitrogen, phosphorus, algae bloom, decomposer

Teacher overview

This is a whole-class role-play for about 24 to 30 students that models eutrophication at the fictional Corvin Lake. Students take roles along a pathway from a farm to a lake and physically pass nutrient tokens down that path. When too many nutrients arrive, the algae "bloom," and the decomposers that later break down the dead algae use up the oxygen tokens that the fish need. The activity shows directly how nitrogen and phosphorus, which are needed nutrients in small amounts, become a pollutant when there are too many, lowering dissolved oxygen and shrinking the fish population.

Activity Directions

  1. Set up five stations around the room with signs: Farm, Runoff, Lake Surface, Lake Bottom, and Fish Zone. Assign roles with cards: 4 students are Farm, 4 are Runoff, 6 are Algae at the Lake Surface, 4 are Decomposers at the Lake Bottom, and the rest are Fish. Give the Farm students a stack of green nutrient tokens, and place a bowl of blue oxygen tokens in the Fish Zone, one token per Fish student to start.
  2. Explain the goal in one sentence: nitrogen and phosphorus are nutrients that algae need in small amounts, and the game shows what happens when far too many wash into a lake.
  3. Round 1, normal levels: the Farm passes one nutrient token per turn to a Runoff student, who carries it to an Algae student at the Lake Surface. Fish move freely, and every oxygen token stays in the Fish Zone bowl. This is a healthy lake.
  4. Round 2, heavy fertilizer: the Farm now passes three nutrient tokens per turn. Any Algae student holding two or more tokens has "bloomed" and taps one Fish student to switch roles and become another Algae, so the bloom grows across the Lake Surface.
  5. Round 3, die-off: once the Lake Surface is full of Algae, each Algae student hands their tokens to a Decomposer at the Lake Bottom. For every two nutrient tokens a Decomposer collects, it removes one oxygen token from the Fish Zone bowl, showing decomposers using oxygen to break down the dead algae.
  6. Watch the oxygen: any Fish student left without an oxygen token must sit down, showing a fish that cannot survive once dissolved oxygen drops, since most fish need it above 5 mg/L.
  7. End the game when the oxygen bowl is empty or after the three rounds, whichever comes first. Count how many Fish students are still standing compared with the start.
  8. Gather the class and debrief using the questions in the Answer Key, linking the tokens and the seated fish back to what happens in real lakes.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key
  1. Debrief question: How are nitrogen and phosphorus both a resource and a pollutant?
    Answer: In small amounts they are nutrients that algae and plants need to grow, but in large amounts they cause algae to overgrow, and the later decay uses up the oxygen other living things need.
  2. Debrief question: What made the fish sit down during the game?
    Answer: The oxygen tokens ran out when the Decomposers used them to break down the dead algae, which stands for dissolved oxygen dropping below the level fish need, about 5 mg/L.
  3. Debrief question: Where did the extra nutrients come from in the game?
    Answer: They came from the Farm and were carried into the lake by the Runoff students, which stands for fertilizer washing off the land during rain.
  4. Debrief question: Name one change that would keep Corvin Lake healthier.
    Answer: Accept answers such as using less fertilizer, planting a strip of plants between the farm and the lake to catch runoff, or spreading fertilizer at times when less rain will wash it away.

Differentiation

Support

Give the Farm and Decomposer students a printed count card ("pass 3," "for every 2 tokens, take 1 oxygen") so the token rules are in hand. Walk the pathway once slowly with no time pressure before starting the timed rounds.

Extension

Add a Buffer Strip role between Runoff and the Lake Surface that can catch one nutrient token per turn. Have students compare how many fish survive with and without the buffer, and explain the difference.

ELL supports

Use picture icons on each station sign (a tractor, a raindrop, green algae, a decomposer, a fish) so roles are clear without heavy reading. Pair each new word with the token it matches: green for nutrient, blue for oxygen.